A sputtering process is typically utilized in the manufacture of integrated circuits (ICs). This process includes the formation of a thin layer of metal on a substrate such as a silicon or a gallium arsenide wafer. Frequently, a sputtering system is utilized which enables a plurality of substrates to be sputtered simultaneously. Such systems include a plurality of process modules each of which provide a high vacuum environment for performing the sputtering process. In addition, each of the process modules include a source target from which material is removed and used for forming the metal layer on the substrate. Consequently, material from the target is depleted through use, which necessitates replacement of the target and defines a life cycle for the target. By way of example, a typical target includes sufficient material to enable the deposition of a 1 micron thick layer on approximately 5,000 to 10,000 substrates before the target becomes depleted, thus defining the end of the target life cycle at which time sputtering is stopped and the depleted target is replaced. Generally, replacement entails venting the process module to atmosphere, manually opening the process module to enable replacement of the target, closing and sealing the process module upon replacement of the target and evacuating the process module to a high vacuum.
Referring to FIG. 1, a conventional sputtering system 10 having a cluster tool configuration is shown as a partial cutaway view. The system 10 includes a central housing 12 having an internal central chamber 14 and a system pump (not shown) for evacuating the central chamber 14 to a high vacuum. The central chamber 14 includes a substrate entry load lock 16 for receiving a substrate 42 and an exit load lock 18 for removal of the substrate 42. The system 10 further includes a plurality of process modules wherein sputtering of substrates is performed. For purposes of illustration, first 20, second 22 and third 24 process modules are shown in FIG. 1. The first 20, second 22 and third 24 process modules are in fluid communication with the central chamber 14. In addition, the first 20, second 22 and third 24 process modules each include a module pump (not shown) for evacuating the process module to a high vacuum and a vent valve (not shown) for venting the process module to atmosphere. Further, the system 10 includes first 26 and second 28 ports which may be used for the addition of other modules.
First 30, second 32, third 34, fourth 36 and fifth 38 module valves are associated with the first 20, second 22 and third 24 process modules and the first 26 and second 28 ports, respectively. The first 30, second 32 and third 34 module valves may each be positioned in an open position which enables its associated process module 20, 22, 24, respectively, to be in fluid communication with the central chamber 14. Alternatively, the first 30, second 32 and third 34 module valves may each be positioned in a closed position which serves to isolate its associated process module 20, 22, 24, respectively, from the central chamber 14.
Furthermore, the system 10 includes a robotic arm 40 located within the central chamber 14. The robotic arm 40 serves to transport the substrate 42 between the entry 16 and exit 18 load locks and between the first 20, second 22 and third 24 process modules as desired.
Various types of devices, fixtures and associated parts (not shown) are utilized in a process module for supporting the substrate 42 and to ensure proper deposition of material on the substrate 42. These include fixtures which serve to support the substrate 42 as the substrate 42 is sputtered known as clamp ring or clamp finger assemblies. Other fixtures include deposition shields which are located adjacent to the substrate 42 and which serve to protect portions of the clamp ring or clamp finger assemblies. Further, fixtures for controlling the angular deposition of material on the substrate 42 known as collimator plates are also utilized. It is noted that many other types of devices, fixtures and tools for ensuring proper deposition of material on the substrate 42 may be used in a process module. Due to their structure and location, many portions of these fixtures are in close proximity to the substrate 42. As such, material from the target which is intended to be deposited on the substrate 42 is also undesirably collected on the fixtures, thus coating the fixtures with target material. This undesirably affects the operation of the fixtures and ultimately the sputtering process. In particular, it has been determined that operation of the fixtures is undesirably affected after the fixtures have been coated with only 2000-3000 microns of material. Consequently, it is desirable to replace each of the fixtures after they have been coated with approximately 2000 microns of material. As such, the life cycle for each of the fixtures is substantially shorter than the life cycle for the associated target. In particular, it has been found that the fixtures may be replaced approximately 5 times for each time that the target is replaced.
In order to access and replace fixtures located in the first process module 20, for example, the first module valve 30 is first closed, thus isolating the first process module 20 from the central chamber 14. The first process module 20 is then vented to atmosphere and manually opened to provide access to the fixtures. The fixtures are then replaced, at which time the first process module 20 is manually closed and sealed. The first module valve 30 may then be opened after evacuation of the first process module 20 to a high vacuum. However, the method used for replacement of fixtures in such a system 10 has disadvantages. A disadvantage is that a substantial amount of time is required, i.e. up to 8 hours or more, to complete the procedure and ultimately achieve high vacuum. As a result, the system 10 does not operate for a substantial amount of time, thus substantially decreasing productivity and increasing operating costs. In addition, the amount of time needed for achieving a high vacuum is substantially increased if new fixtures are used which have not previously been subjected to vacuum conditioning to reduce surface outgassing to a desired level. Further, exposure of the first process module 20 to atmosphere frequently requires a requalification of film properties before the system 10 may be certified as suitable for production. Additionally, since the fixtures may be replaced as many as 5 times for each time that the target is replaced, the amount of time that the system 10 does not operate is further increased, thus further reducing productivity and increasing operating costs.
Another type of sputtering system is described in U.S. Pat. No. 4,909,695, which issued to Hurwitt, et al. and is assigned to Materials Research Corporation, the assignee herein. This patent discloses a production sputtering system in which a coated wafer holding fixture may be replaced through a load lock normally used for substrate entry and exit. However, although this system enables the process module to remain under vacuum, this system does not provide for vacuum conditioning of the wafer holding fixture to reduce surface outgassing. In addition, the configuration of the system is such that only the wafer holding fixture may be replaced. Further, replacement of the wafer holding fixture is performed manually, thus substantially increasing the time needed for replacing the fixture which results in substantially reduced productivity and increased costs.
Therefore, it is an object of the present invention to provide a sputtering system having an on board service module which provides for vacuum conditioning of fixtures which are to be used in a process module before the fixtures are installed in the process module. It is a further object of the present invention to provide a sputtering system having an on board service module which enables the replacement of more than one type of fixture. It is a still further object of the present invention to provide a sputtering system having an on board service module which enables automated replacement of a coated fixture. Additionally, it is an object of the present invention to provide for a sufficient number of replacement fixtures and associated parts so that venting and opening of a process module is not necessary until a source target is replaced.